1. Field of the Invention
The present invention relates to a method for decomposing halogenated aliphatic hydrocarbon compounds or aromatic compounds, a method for cleaning a medium contaminated with at least one of these compounds, and an apparatus to be used for the same.
2. Related Background Art
As the industry develops, a variety of halogenated aliphatic hydrocarbon compounds and aromatic compounds have been used in large amounts, posing severe disposal problems. A variety of halogenated aliphatic hydrocarbon wastes have been causing environmental problems, e.g., pollution of natural environments, and a great deal of efforts have been made to solve these problems.
For example, a combustion process has been proposed to decompose chlorinated aliphatic hydrocarbon compounds, where the compounds are first adsorbed to activated charcoal or the like and then burned.
Also techniques of using an oxidizing agent or a catalyst for decomposing chlorinated aliphatic hydrocarbon compounds have been proposed. Specific examples include a process of decomposing harmful hydrocarbons by means of ozone (Japanese Patent Application Laid-Open No. 3-38297), a process of wet oxidation decomposition at high temperature under high pressure and a process of oxidization decomposition with hydrogen peroxide or a salt of iron (Japanese Patent Application Laid-Open No. 60-261590).
There is also a proposed process wherein sodium hypochlorite is used as an oxidizing agent (U.S. Pat. No. 5,611,642), or a combination use of sodium hypochlorite and UV irradiation (U.S. Pat. No. 5,582,741). There is also a proposed process where a suspension of a photocatalyst (fine particles of an oxide semiconductor such as titanium oxide) in liquid chlorinated aliphatic hydrocarbons is prepared under alkaline conditions and decomposed by light irradiation (Japanese Patent Application Laid-Open No. 7-144137).
Also, a photolysis process of decomposing chlorinated aliphatic hydrocarbon compounds by irradiating with UV light in a gaseous phase without an oxidizing agent is proposed (H. Seki et al, xe2x80x9cContaminated Groundwater and Soil: Present Condition and Countermeasurexe2x80x9d, ed. by Kansai Branch of Japan Water Environment Society and Environmental Technology Research Institute, 1995; Japanese Patent Application Laid-Open No. 8-243351).
It is known that chlorinated aliphatic hydrocarbons such as trichloroethylene (TCE) and polychloroethylene (PCE) are decomposed by microorganisms aerobically or anaerobically, and there were attempts to decompose such compounds and purify the natural environment by such a microbial process.
Japanese Patent Application Laid-Open No. 8-141367 discloses a process of decomposing CFCs by mixing them with fuel such as alcohol or ether and burning them in the presence of a catalyst.
U.S. Pat. No. 5,393,394 discloses a process of decomposing CFCs by exposing them to ultraviolet light either directly or after dissolving them into a solvent.
Japanese Patent Application Laid-Open No. 3-074507 discloses a method for reductively decomposing gaseous chlorofluorohydrocarbon by contacting it with an electrode in an electrolytic vessel.
As proposed techniques for decomposing the other organic compounds, e.g., hardly decomposable aromatic compounds such as those having a biphenyl bond and/or a biphenyl skeleton, there are (1) combustion, (2) decomposition by UV or ionizing radiation exposure and (3) decomposition using microorganisms. In Japan, only method (1) is in practice.
As a method for decomposing biphenyl compounds, there is a process wherein such compounds are decomposed by irradiation with UV light directly or after dissolving them into a solvent. For example, Japanese Patent Publication No. 52-47459 discloses a method of rendering polychlorinated biphenyl harmless by dissolving it into alkaline alcohol, removing oxygen from the solution and then exposing the solution to ionizing radiation or UV light.
Other known techniques for rendering PCB harmless include those described in Japanese Patent Laid-Open Application No. 62-191095 and Japanese Patent Publication Nos. 49-45027 and 57-166175.
Japanese Patent Application Laid-Open No. 7-000819 discloses a method for removing polychlorinated biphenyl etc. by utilizing the photocatalytic activity of titanium oxide.
Japanese Patent Application Laid-Open No. 8-000759 describes a photodecomposition apparatus and method for degrading polychlorinated biphenyl.
Methods for degrading biphenyl compounds by utilizing microorganisms have been disclosed by, for example, Japanese Patent Application Laid-Open No. 8-229385.
The inventors of the present invention have studied the above-mentioned methods for decomposing halogenated aliphatic hydrocarbon and aromatic compounds, and found out that they have, or involve problems, concluding that there are still strong needs for eco-friendly technology for decomposing halogenated aliphatic hydrocarbon compounds or aromatic compounds. In a study for achieving the above objects, the inventors found that functional water, e.g., acidic functional water, which is obtained through electrolysis of water and of which sterilizing effect (Japanese Patent Application Laid-Open No. 1-180293) and cleansing effect for the surface of semiconductor wafers (Japanese Patent Application Laid-Open No. 7-51675) have been reported, can remarkably accelerate the decomposition of halogenated aliphatic hydrocarbon compounds or aromatic compounds under light irradiation.
The present invention is based on this finding.
An object of the present invention is to provide a method of efficiently decomposing halogenated aliphatic hydrocarbon compounds or aromatic compounds in a more eco-friendly manner with less possibility of producing decomposition products that will cause another environmental contamination, as well as an apparatus to be used for such a method.
Another object of the present invention is to provide a method for efficiently purifying an exhaust containing halogenated aliphatic hydrocarbon compounds or aromatic compounds and an apparatus to be used for such a method.
According to an aspect of the present invention, there is provided a method for decomposing halogenated aliphatic hydrocarbon compounds or aromatic compounds, which comprises the steps of:
(i) contacting a halogenated aliphatic hydrocarbon compound or aromatic compound with functional water under irradiation with light, the functional water being produced by electrolysis of an aqueous electrolyte solution; and
(ii) neutralizing wastewater from the step (i).
According to another aspect of the present invention, there is provided a method for decomposing halogenated aliphatic hydrocarbon compounds or aromatic compounds, which comprises the steps of:
(i) bringing the halogenated aliphatic hydrocarbon compound or aromatic compound into contact with functional water containing hypochlorous acid under irradiation with light; and
(ii) neutralizing wastewater from the step (i).
According to still another embodiment of the present invention, there is provided a method for decomposing halogenated aliphatic hydrocarbons or aromatic compounds, which comprises the steps of:
(i) bringing a halogenated aliphatic hydrocarbon compound or aromatic compound into contact with functional water under irradiation with light, the functional water being produced by electrolysis of an aqueous electrolyte solution; and
(ii) bringing wastewater from the step (i) into contact with a microorganism which can decompose a compound contained in wastewater from the step (i).
According to still another aspect of the present invention, there is provided a method for decomposing halogenated aliphatic hydrocarbon compounds or aromatic compounds, which comprises the steps of:
(i) bringing a halogenated aliphatic hydrocarbon compound or aromatic compound into contact with functional water under irradiation with light, the functional water being produced by electrolysis of an aqueous electrolyte solution; and
(ii) bringing wastewater from the step (i) into contact with a microorganism which can decompose a compound contained in the wastewater from the step (i).
According to still another aspect of the present invention, there is provided a method for purifying a medium polluted with at least one of halogenated aliphatic hydrocarbon compounds and aromatic compounds, which comprises the steps of:
(i) contacting the contaminated medium with functional water under irradiation with light, the functional water being produced by electrolysis of an aqueous electrolyte solution; and
(ii) neutralizing wastewater from the step (i).
According to still another aspect of the present invention, there is provided a method for purifying a medium polluted with at least one of halogenated aliphatic hydrocarbon compounds and aromatic compounds which comprises the steps of:
(i) contacting the contaminated medium with functional water containing hypochloric acid under irradiation with light; and
(ii) neutralizing wastewater from the step (i).
According to still another aspect of the invention, there is provided an apparatus for decomposing at least one of halogenated aliphatic hydrocarbon compounds and aromatic compounds, which comprises:
(1) an electrolysis tank having an anodic and cathodic compartments partitioned with a diaphragm, a pair of electrodes provided in the compartments respectively, and a power source to apply a potential to the electrodes,
(2) means for supplying an aqueous electrolytic solution to the electrolysis tank,
(3) means for irradiating light at least to the anodic compartment of the electrolysis tank,
(4) means for supplying the halogenated aliphatic hydrocarbon compound or the aromatic compound to be decomposed to the anodic compartment in the electrolysis tank, and
(5) means for mixing wastewater discharged from the anodic compartment of the electrolysis tank with a liquid flowing out from the cathodic compartment of the electrolysis tank.
According to still another aspect of the invention, there is provided an apparatus for decomposing halogenated aliphatic hydrocarbon compounds or aromatic compounds, which comprises
(1) a decomposition treatment tank,
(2) means for supplying functional water to the decomposition treatment tank, the functional water being produced around an anode when an aqueous electrolytic solution is electrolyzed in an electrolytic tank having two compartments partitioned by a diaphragm and provided with an anode and a cathode respectively,
(3) means for supplying the halogenated aliphatic hydrocarbon compound or the aromatic compound to be decomposed to the decomposition treatment tank,
(4) means for irradiating light to the decomposition treatment tank, and
(5) means for mixing wastewater discharged from the decomposition treatment tank with alkaline water produced around the cathode by the electrolysis of the aqueous electrolytic solution.
According to still another aspect of the invention, there is provided an apparatus for decomposing halogenated aliphatic hydrocarbon compounds or aromatic compounds, which comprises
(1) a decomposition treatment tank for holding functional water containing hypochlorous acid,
(2) means for supplying the halogenated aliphatic hydrocarbon compound or the aromatic compound to be decomposed to the decomposition treatment tank,
(3) means for irradiating light to the decomposition treatment tank, and
(4) means for mixing wastewater discharged from the decomposition treatment tank with an alkaline aqueous solution.
According to still another aspect of the invention, there is provided an apparatus for decomposing halogenated aliphatic hydrocarbon compounds or aromatic compounds, which comprises
(1) an electrolysis tank having an anodic and cathodic compartments partitioned with a diaphragm, a pair of electrodes each provided in each component, and a power source to apply a potential to the electrodes,
(2) means for supplying an aqueous electrolytic solution to the electrolysis tank,
(3) means for irradiating light at least to the anodic compartment of the electrolysis tank,
(4) means for supplying the halogenated aliphatic hydrocarbon compound or the aromatic compound to be decomposed to the anodic compartment in the electrolysis tank, and
(5) means for mixing wastewater discharged from the anodic compartment of the electrolysis tank with a microorganism which can degrade a halogenated acid.
According to still another aspect of the invention, there is provided an apparatus for decomposing halogenated aliphatic hydrocarbon compounds or aromatic compounds, which comprises
(1) a decomposition treatment tank,
(2) means for supplying functional water to the decomposition treatment tank, where the functional water is produced around an anode when an aqueous electrolytic solution is electrolyzed in an electrolytic tank having an anodic and cathodic compartments partitioned by a diaphragm and provided with an anode and a cathode respectively,
(3) means for supplying the halogenated aliphatic hydrocarbon compound or the aromatic compound to be decomposed to the decomposition treatment tank,
(4) means for irradiating light to the decomposition treatment tank, and
(5) means for mixing wastewater discharged from the decomposition treatment tank with a microorganism which can degrade a halogenated acid.
According to still further aspect of the invention, there is provided an apparatus for decomposing halogenated aliphatic hydrocarbon compounds or aromatic compounds, which comprises
(1) a decomposition treatment tank for holding the functional water containing hypochlorous acid,
(2) means for supplying the halogenated aliphatic hydrocarbon compound or the aromatic compound to be decomposed to the decomposition treatment tank,
3) means for irradiating light to the decomposition treatment tank, and
(4) means for mixing wastewater discharged from the decomposition treatment tank with a microorganism which can degrade a halogenated acid.
According to the above-mentioned embodiments of the present invention, halogenated aliphatic hydrocarbon compounds or aromatic compounds can be decomposed with a lessened burden to the environment.
Further, according to the embodiments of the present invention, a medium contaminated with halogenated aliphatic hydrocarbon compounds or aromatic compounds or both can be purified with a lessened burden to the environment.
Still, according to the embodiments of the present invention halogenated aliphatic hydrocarbon compounds or aromatic compounds or both can be decomposed more safely and efficiently.